(1) Field of the Invention
This invention relates to an electrically conductive web which may be fabricated into floor mats, curtains, clothing, and other articles. The web exhibits controlled electrical properties which permit it to be effectively used to discharge statically charged objects coming into contact with the semiconductive surface layer.
(2) Description of the Prior Art
A person may become statically charged to a potential of up to 30,000 volts. If a charged person comes into contact with a highly conductive, well-grounded surface, a substantially instantaneous spark discharge will result. Such static discharges can be both uncomfortable and hazardous.
Conventional materials for controlling static electricity are commercially available and are used for a variety of purposes. Typical uses include the elimination of static shock discomfort and spark avoidance in hazardous environments such as munitions plants and medical operating rooms. These materials may also be fabricated into floor mats for use with computer terminals and other static sensitive electronic equipment.
There are two prior approaches to conductive webs used for control of static electricity.
One prior art approach is to provide a mat which is more conductive than applicants'. U.S. Pat. No. 3,406,126 issued Oct. 15, 1968 to I. Litant is an example of a highly conductive web. Highly conductive mats are useful for preventing build up of static charge. However, these webs are usually too conductive to be used for disspiating static charge already accumulated on personnel. A highly conductive floor covering or web will permit substantially instantaneous discharge which may result in hazardous spark discharge.
The second conventional approach to static control involves the use of highly resistive webs. U.S. Pat. No. 3,891,786 issued Oct. 15, 1973 to C. Conklin is a representative example of a carbon loaded prior art web. These webs are usually sufficient to control the discharge of accumulated static. However, such webs usually exhibit electrical characteristics which are dependent on the ambient humidity. In most applications, it is desirable to have a conductive web with electrical discharge properties which are independent of the moisture level of the operating environment.
Applicants' web provides a means for both preventing the build-up of static charge as well as the rapid and safe discharge of accumulated static electricity.
Applicants' web can discharge a statically charged person from 30,000 volts to ground potential within one or two seconds of contacting the mat. However the controlled electrical characteristics of the mat structure also insure sufficient resistivity to prevent spark discharge.
Applicants' novel web structure differs from prior art structures, and exhibits an unusual and desirable electrical discharge property. When applicants' web is grounded and a static charge is applied to the web through an insulative material, applicants' mat exhibits a faster discharge rate than a grounded metal plate, under similar conditions. Although the reason for this anomalous behavior is not known, it is a desirable property since it insures that a statically charged person wearing synthetic soled shoes will be rapidly discharged in spite of the insulative nature of his shoes.